Math Problem Statement

Differentiate f(x) = √x from first principles given that f'(x) = lim (h → 0) [(f(x+h) - f(x))/h], h ≠ 0.

Solution

We are tasked with differentiating f(x)=xf(x) = \sqrt{x} using the first principles of differentiation, as given by the formula:

f(x)=limh0f(x+h)f(x)hf'(x) = \lim_{h \to 0} \frac{f(x+h) - f(x)}{h}

Here, f(x)=xf(x) = \sqrt{x}, so let’s substitute that into the limit expression:

f(x)=limh0x+hxhf'(x) = \lim_{h \to 0} \frac{\sqrt{x+h} - \sqrt{x}}{h}

To simplify this expression, we multiply the numerator and denominator by the conjugate of the numerator:

f(x)=limh0x+hxhx+h+xx+h+xf'(x) = \lim_{h \to 0} \frac{\sqrt{x+h} - \sqrt{x}}{h} \cdot \frac{\sqrt{x+h} + \sqrt{x}}{\sqrt{x+h} + \sqrt{x}}

This gives:

f(x)=limh0(x+h)2(x)2h(x+h+x)f'(x) = \lim_{h \to 0} \frac{(\sqrt{x+h})^2 - (\sqrt{x})^2}{h(\sqrt{x+h} + \sqrt{x})}

Simplifying the numerator:

f(x)=limh0(x+h)xh(x+h+x)=limh0hh(x+h+x)f'(x) = \lim_{h \to 0} \frac{(x+h) - x}{h(\sqrt{x+h} + \sqrt{x})} = \lim_{h \to 0} \frac{h}{h(\sqrt{x+h} + \sqrt{x})}

Cancel the hh in the numerator and denominator:

f(x)=limh01x+h+xf'(x) = \lim_{h \to 0} \frac{1}{\sqrt{x+h} + \sqrt{x}}

Now, as h0h \to 0, x+hx\sqrt{x+h} \to \sqrt{x}. So the limit becomes:

f(x)=12xf'(x) = \frac{1}{2\sqrt{x}}

Thus, the derivative of f(x)=xf(x) = \sqrt{x} from first principles is:

f(x)=12xf'(x) = \frac{1}{2\sqrt{x}}

Would you like any further clarification or a deeper explanation of any steps?

Here are 5 related questions to explore:

  1. How would you apply first principles to differentiate f(x)=x2f(x) = x^2?
  2. What is the geometric interpretation of the derivative obtained for f(x)=xf(x) = \sqrt{x}?
  3. How do higher-order derivatives work in first principles for more complex functions?
  4. Can first principles be used to differentiate trigonometric functions, like sin(x)\sin(x)?
  5. How does the concept of limits apply when calculating derivatives?

Tip: When simplifying expressions using first principles, multiplying by the conjugate is a common strategy to handle square roots effectively.

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Math Problem Analysis

Mathematical Concepts

Differentiation
First Principles of Differentiation
Limits

Formulas

f'(x) = lim (h → 0) [(f(x+h) - f(x))/h]
f'(x) = lim (h → 0) [(√(x+h) - √x)/h]

Theorems

Definition of Derivative

Suitable Grade Level

Grades 11-12